# Sound: missed test questions

#### Dx

1) A sample of Co2 contains 3.01x10^23 molecules at STP. what volume does this sample occupy?
I have the multiple choice answers but need help explaining why you chose that answer.

11.2L
44.8L
32.7L

2) a 25L container hold H gas at gauge pressure 1.25atm and temo 0 degrees celcius. whats mass of H in this container

2.8g
4.2g
5.6g

3) An ideal gas has density of 1.75kg/m^3 at gauge pressure 160kPa. what must be the gauge pressure isf density of 1 kg/m^3 is desired at the same temp?

356kPA
280kPA
48KPa

4) an ideal gas in container of volume 100cm^3 at 20 degrees C has pressure of 100N/m^2. determine the number of gas molecules in the container

6x10^23
2.5x10^18
5.2x10^18

I am not going to put my work here since ive already missed them. I cant go on not understanding why or what these answers were. I have gone back to re-read the chapter on this and still unclear with the ideal gas law, i know its said to be simple but its not clicking here. I dont need a long explaination just the answer you got and briefly how you derived it. If you feel you dont have to answer this cause it vilates so rules its like i said "Its not homework but missed test questions that for my own personnel conquest I must try to solve but need your help, plz" Please understand I hold each of you in the highest respect and thank you for all youve done. Its really been a great help for me to better understand this subject.
I applaude you all!
Dx

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#### Tom Mattson

Staff Emeritus
Gold Member
You use the same equation for all of these: PV=nRT

P=absolute pressure
V=volume
n=# of moles
R=ideal gas constant
T=temp (in oK)

#### Tom Mattson

Staff Emeritus
Gold Member
Hey, check this out:

http://www-tech.mit.edu/Chemicool/idealgas.html [Broken]

Neato.

Last edited by a moderator:

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